This project deals with the problem of the detection, quantitation and operation of RNA tumor virus genes in cellular DNA. The frequency of proviral sequences related to avian leukoses, sarcoma and "endogenous" oncornaviruses will be measured in normal and neoplastic tissues in chickens by means of RNA-DNA hybridization reactions between the 60-70 S viral RNA genome and cellular DNA. A technique of competitive hybridization will be developed as a method for studying sequence relatedness between the several types of avian oncornaviruses and for detecting RNA transcripts of proviral genes in cells. Bibliographic references: Neiman, P.E., Purchase, H.G. and Okazaki, W.: Chicken leukosis virus genome sequences in DNA from normal chick cells and virus-induced bursal lymphomas. Cell 4: 311-319, 1975. Neiman, P.E., Wright, S.E. and Purcase, H.G.: Studies of the interrelationship of chicken leukosis virus and host cell genomes by RNA-DNA hybridization. Cold Spring Harbor Symp. Quant. Biol. 39: 875- 883, 1975.